This application is based on Application No. 029787 filed in Japan on Feb. 6, 2001, the content of which is incorporated hereunto by reference.
The present invention relates to a charger in which a plurality of batteries are connected in parallel with each other and are charged together.
A charger in which a plurality of batteries are connected in parallel with each other and are charged, can charge the plurality of batteries through a simple circuit. Besides, since voltages of the plurality of batteries connected in parallel with each other become equal to each other, this charger has also a feature that while overcharging of all the batteries is prevented, they can be fully charged. However, when the plurality of batteries having a difference in residual capacity are connected in parallel with each other and are charged together, there is a case where full charge is erroneously detected. For example, when a battery having a residual capacity close to 100% and a battery having a residual capacity close to 0% are charged together, although only the battery having the residual capacity of 0% is charged, at this time, there is a case where a characteristic is shown in which an ascent curve of battery voltage is lowered from the peak voltage by xe2x88x92xcex94V. In the method of judging the full charge by detecting that the voltage is lowered from the peak voltage by xe2x88x92xcex94V, when this voltage characteristic occurs, it is erroneously judged that the full charge has been attained, and charging is ended. Thus, it becomes impossible to fully charge all the batteries.
This defect can be resolved by a method in which when xe2x88x92xcex94V is detected, charging is stopped, and then, after charging is suspended for a specified time, charging is resumed, and xe2x88x92xcex94V is again detected to judge the full charge. That is, the defect can be resolved by the method in which xe2x88x92xcex94V is detected plural times and the full charge is judged. However, in the method in which the full charge is judged by detecting xe2x88x92xcex94V plural times, since charging is further performed after all the batteries are fully charged, there is a case where the battery is overcharged. Besides, there occurs a defect that the overcharge of the battery often occurs and the battery is deteriorated. This is because the erroneous detection of the full charge through xe2x88x92xcex94V occurs only when the plurality of batteries in a specific state are charged, and it does not occur when the plurality of batteries not having a large difference in residual capacity are charged in parallel.
The present invention has been developed in order to solve the defects. A primary object of the invention is to provide a charging method and a charger in which batteries having a difference in residual capacity can be normally fully charged without overcharging a fully charged battery.
In a charging method of the invention, a plurality of batteries are connected in parallel with each other and are charged, a battery voltage under charging is detected, xe2x88x92xcex94V by which the battery voltage is lowered from a peak voltage is detected, and full charge is judged. Further, in the charging method of the invention, after the full charge is detected from detection that the battery voltage is lowered from the peak voltage by xe2x88x92xcex94V, charging is stopped, and currents flowing to the batteries connected in parallel are detected in a state where charging is stopped. When all the batteries are in a full charge state, since voltages of all the batteries are equal to each other, the currents do not flow. However, when all the batteries are not fully charged and there is a difference in residual capacity, a voltage difference is generated and the currents flow to the batteries connected in parallel. Accordingly, when the currents flow to the batteries, it is judged that the full charge has not been attained, and charging is resumed. The battery to be charged by the method of the invention is a battery in which the full charge can be detected by xe2x88x92xcex94V, for example, a nickel-hydrogen battery or a nickel-cadmium battery. The number of times recharging is performed is preferably made one.
A charger of the invention comprises a charging power source portion for charging a plurality of batteries connected in parallel with each other, a charging switch for connecting the charging power source portion to the batteries connected in parallel, current detection portions for detecting currents of the batteries connected in parallel, and a charging control portion for controlling the charging switch so as to turn it on or off by detecting battery voltages. The charging control portion detects xe2x88x92xcex94V as a drop of the battery voltage from the peak voltage and detects the full charge, and further, in the state where the charging switch is turned off, the charging control portion again detects the full charge state of the batteries through the current values of the current detection portions.
The foregoing charging method and device have a feature that batteries having a difference in residual capacity can be normally fully charged without overcharging a fully charged battery. This is because after the full charge is detected through xe2x88x92xcex94V by which the battery voltage is lowered from the peak voltage, charging is stopped, and currents flowing to the batteries connected in parallel are detected in the state where charging is stopped, and the full charge of the batteries is again detected. In the above charging method and charger, the full charge is not judged in such a manner that after xe2x88x92xcex94V is detected and a judgment of full charge is made, charging is further performed to detect xe2x88x92xcex94V plural times, but it is possible to accurately judge whether all the batteries are fully charged in the state where charging is stopped. Accordingly, a fully charged battery is not overcharged or when there is a battery which is not fully charged, charging is resumed and the batteries can be normally fully charged.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.